1. Field of the Invention
The present invention relates to the arrangement of thermal print heads in thermal recording devices with related methods and devices for aligning such print heads in these recording devices. More specifically, the invention relates to the arrangement of multiple narrow thermal print heads in wide format printers. The methods described in the present invention specifically relate to the alignment of such print heads in a manufacturing process or in service.
2. Description of the Related Art
In a thermal transfer printer, a transfer ribbon typically having a polyester backing coated on one side with a heat-transferable ink layer is interposed between the surface of a non sensitized paper and a thermal print head having a line of very small heater elements. When an electrical pulse is applied to a selected subset of the heater elements, localized melting and transfer of the ink to the paper occurs under the energized elements, resulting in a corresponding line of dots being transferred to the paper.
Thermal print heads in such thermal transfer printers are commonly composed of a plurality of linear thermal head segments or "tiles" aligned in the width direction of a recording medium sheet, perpendicular to the feeding direction or the lengthwise direction of the recording medium sheet, so that a predetermined number of thermal print elements of adjacent tiles overlap to cover the entire width of the recording medium sheet.
A typical thermal head segments arrangement, using the overlapping technique conforming to the Related Art, as described in U.S. Pat. No. 5,450,099 to Stephenson et al., is shown in FIG. 1.
Stephenson et al., describes in their patent a method of an apparatus for sequential printing lines of image pixels in the thermal printing of a two-dimensional image on a wide format media paper, employing a print head arrangement of the type comprising a plurality N of linear thermal print head segments heaving a set n of thermal print elements.
He uses an alternating, staggered pattern in first and a second rows of N1 and N2 print head segments arranged across the media in a print line direction such that respective subsets of n1 thermal print elements of the adjacent ends of the N1 and N2 print head segments arranged in the first and second rows, overlap one another in the print line direction.
However, a drawback of this overlapping method of print head arrangement is that it uses more thermal print elements than necessary for printing the information, thus increasing the complexity and the price of the print head.
Another major drawback of Stephenson's patent consists in the fact that the alignment of thermal print elements is very difficult to accomplish in both the manufacturing and servicing processes. This is due to the independent positioning and fixing of each print head segment, which can be displaced in two directions and can be rotated in the fixation plane. This creates a need for more operations to obtain a parallel arrangement between two adjacent thermal print line segments, the exact overlapping of the thermal print elements, and the linearity of thermal print segments of each row. This will also increase the cost of manufacturing or servicing.